Wednesday, September 14, 2011

New paper shows water vapor feedback is negative, not positive as claimed by IPCC

A paper published today in the journal Environmental Research Letters shows that water vapor feedback to the climate system is negative (causes cooling due to increased cloud formation) rather than positive as claimed by the IPCC and fellow alarmists. Warmists claim a doubling of CO2 levels could result in a mere 1C global temperature change, with positive water vapor feedback supposedly causing much more temperature increase. However, this new paper (and others) finds that feedback from the water cycle is instead negative and would lead to offsetting global cooling.

Climate forcing and response to idealized changes in surface latent and sensible heat

George A Ban-Weiss1,3, Govindasamy Bala2, Long Cao1, Julia Pongratz1 and Ken Caldeira1

Land use and land cover changes affect the partitioning of latent and sensible heat, which impacts the broader climate system. Increased latent heat flux to the atmosphere has a local cooling influence known as 'evaporative cooling', but this energy will be released back to the atmosphere wherever the water condenses. However, the extent to which local evaporative cooling provides a global cooling influence has not been well characterized. Here, we perform a highly idealized set of climate model simulations aimed at understanding the effects that changes in the balance between surface sensible and latent heating have on the global climate system. We find that globally adding a uniform 1  W m − 2 source of latent heat flux along with a uniform 1  W m − 2 sink of sensible heat leads to a decrease in global mean surface air temperature of 0.54 ± 0.04 K. This occurs largely as a consequence of planetary albedo increases associated with an increase in low elevation cloudiness caused by increased evaporation. Thus, our model results indicate that, on average, when latent heating replaces sensible heating, global, and not merely local, surface temperatures decrease.


Sensible heat
When an object is heated, its temperature rises as heat is added. The increase in heat is called sensible heat. Similarly, when heat is removed from an object and its temperature falls, the heat removed is also called sensible heat. Heat that causes a change in temperature in an object is called sensible heat.

Latent heat
All pure substances in nature are able to change their state. Solids can become liquids (ice to water) and liquids can become gases (water to vapor) but changes such as these require the addition or removal of heat. The heat that causes these changes is called latent heat.

Latent heat however, does not affect the temperature of a substance - for example, water remains at 100°C while boiling. The heat added to keep the water boiling is latent heat. Heat that causes a change of state with no change in temperature is called latent heat.

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